1. Field of the Invention
The present invention relates to a semiconductor composite device and a method of manufacturing the same such that a microelectromechanical system (MEMS) and a semiconductor device can be easily formed on the same substrate.
2. Description of the Related Art
The research and development of microelectromechanical systems (MEMS) begun in the 1970's has at present been developed in various fields such as sensor devices, actuators, optical devices, bio-devices, RF devices, power devices, etc., and some of the devices such as acceleration sensors and micromirror devices have already been commercialized and have come to be seen in daily life.
Attendant on such a progress, conversion of ordinary devices into the so-called composite devices, such as incorporation of a peripheral circuit into an originally monofunctional MEMS device so as to impart a system function to the device and incorporation of an MEMS into other device so as to enhance the added value, has been conducted vigorously in recent years. This is greatly contributed to by the fact that, since an MEMS is fundamentally based on a semiconductor process, it is possible to utilize such techniques as SiP (System in Package) and SoC (System on Chip) which have been conducted in converting other semiconductor devices into composite devices. As for the SoC, particularly, the MEMS's in recent years produced by application of advanced processes are advantageous in that their footprints have been reduced and they can be easily handled at the time of mounting onto substrates. For example, in the case of RF-MEMS and the like of which research and development have recently progressed rapidly, there is a need to finally assemble such a device into the form of a module as a communication function, so that the device is liable to share in the benefit of consolidation into one chip through SoC.
However, at the time of forming an MEMS device and other devices on the same wafer as SoC, the manufacturing method is greatly restricted by the materials and sizes of the MEMS device. Particularly, in the case of putting an MEMS into a conventional standardized process, the insertion of an MEMS process and modifications of the conventional process cause variations in the characteristics of electronic circuitry. This has a great influence on the process of forming electronic circuits which will be enhanced in performance now on, and it can be easily supposed that the influence becomes an obstacle in mounting the MEMS device and advanced semiconductor devices together.
Therefore, in many cases, it has been tried to composing functions by SiP or other similar techniques (joining of wafers, etc.). For example, it has been realized to join a semiconductor device wafer to an MEMS wafer comparatively reduced in the increase of film thickness by such a configuration that a layer provided with semiconductor devices can later be separated from a substrate (see, for example, Japanese Patent Laid-open No. 2004-221285). However, according to the SiP or the like method, it may be difficult to make the most of the composite device of semiconductor devices and MEMS produced by an advanced process, due for example to the need for alignment margins at the time of joining.
On the other hand, of manufacturing methods based on the use of SoC, the main method is that MEMS devices are formed on wirings in an electronic circuit by use of a material which can be formed at such a low temperature region as not to damage the wiring layer. However, if the low temperature formable material is difficult to be used in common in other devices' manufacturing steps, the cost is raised accordingly. Besides, in many cases, it may be difficult to obtain desired characteristics on the basis of material constants, and reliability may be poor. The mounting of MEMS devices and other devices on the same wafer is possible on a theoretical basis, but, in consideration of cost and reliability, the practicality of such an approach is considered to differ case by case.
Besides, a manufacturing method has been proposed in which an electronic circuit forming area is preliminarily covered with a protective film, which is removed after the formation of an MEMS device, then an electronic circuit is formed, and the MEMS device and the electronic circuit are connected to each other by a wiring (see, for example, Japanese Patent Laid-open No. Hei 9-162462). However, since the MEMS device in the state of having a comparatively large stepped portion is put into a former step in forming the electronic circuit (FEOL: Front End Of Line) where strict size control is performed, it can be easily supposed that there arise such problems as dimensional scattering in lithography, etching stringer problem, etc. In addition, there is a need to modify the manufacturing process on the basis of each electronic circuit with which the MEMS device is mounted, so that it is impractical to apply such an approach to a diversity of kinds of products.